Lecture 10 - The Pennsylvania State University Department...

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Unformatted text preview: The Pennsylvania State University Department of Civil and Environmental Engineering Lecture 10 Horizontal Alignment (Part 2) CE 321: Highway Engineering Fall 2007 Horizontal Sight Distance Horizontal Sight Distance Stopping Sight Distance Considerations for Horizontal Curves Source: Figure 3.14 from MKW Stopping Sight Distance for Horizontal Curves SSD = Rv s 180 s = 180 ( SSD ) Rv Rv = radius to vehicle's traveled path (radius to the middle of the innermost lane) s = the angle subtended by an arc equal to the SSD distance Stopping Sight Distance for Horizontal Curves Ms = Rv 1 - cos 90 (SSD) Rv Rv - Ms Rv SSD = cos-1 90 Rv Rv = radius to vehicle's traveled path (radius to the middle of the innermost lane) SSD = stopping sight distance (ft) Ms = middle ordinate distance (ft) Source: www.answers.com Source: www.roadstothefuture.com Source: www.roadstothefuture.com Example Problem 1 Given a design speed = 60 mi/hr SSD = 570 ft Radius = 2300 ft at centerline Determine the minimum setback for an obstruction from the edge of the pavement Example 1 (con't) Radius at the Centerline of the Travel Lane R = 2300 - (12/2) = 2294 ft Example 1 (con't) Solution: 90( SSD) M s = Rv 1 - cos R v 90(570) = 17.68 ft M s = 22941 - cos (2294) Clear from Edge of Pavement 17.68 - 6 = 11.68 ft Transition from Tangent Section to a Curved Section Rotate the Pavement Cross-Section Superelevation Runoff-Runout Exhibit 3-37, AASHTO Green Book Transitions Tangent Runout - length needed to accomplish change in outside lane cross slope from normal slope rate to zero. Superelevation Runoff - the length of roadway needed to accomplish a change in outside lane cross slope of zero to full superelevation. Spiral Curves Alternative transition method. Radius of the spiral at Tangent to Spiral (TS) is infinity. Radius of the spiral at Spiral to Curve (SC) is the radius of the curve (therefore the radius changes as the vehicle moves along the spiral). Spiral Description Spiral Curves The radius of a spiral, at any point, is inversely proportional to its length (constantly changing) The Degree of curve of the spiral increases at a uniform rate from zero at the T.S. to the Degree (D) of circular arc at the S.C. ...
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This note was uploaded on 04/11/2008 for the course C E 321 taught by Professor Pietrucha,martinkeller,michaelwi during the Spring '07 term at Pennsylvania State University, University Park.

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Lecture 10 - The Pennsylvania State University Department...

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